1. Field of the Invention
Embodiments of the present invention relate to communication control and, more particularly, to a communication control technique to be used when connecting a peripheral device via a connector having a plurality of independent data buses.
2. Description of the Related Art
USB 3.0 (Universal Serial Bus 3.0 Specification, Revision 1.0, Nov. 12, 2008) implements a maximum data transfer rate of 5 Gbps and has been developed recently as a next-generation high-speed interface. USB 3.0 includes a SuperSpeed (SS) mode (5 Gbps). USB 3.0 also supports the three transfer modes for use with existing USB 2.0: High-Speed (480 Mbps) mode, Full-Speed (12 Mbps) mode, and Low-Speed (1.5 Mbps) mode.
In general, the bus architecture of a USB host device is configured to branch from one host controller to a plurality of connectors. When a plurality of devices are connected, the host controller allocates 5-Gbps of bandwidth to the plurality of connected devices, which share the bandwidth to implement data transfer to each device. For this reason, when the plurality of devices are transferring data simultaneously, the data transmission bandwidth assigned to each device becomes narrower.
Nevertheless, transfer rates of recording media interfaces have increased. For example, the SD card standard SDXC (eXtended Capacity) defines a plurality of transfer modes and is supposed to implement data transfer at 2.4 Gbps in its fastest transfer mode. SDXC is also downward compatible with existing SDHC (High Capacity) and SD.
In this case, as shown in FIG. 13, a device 2000 may be assumed, which includes a card interface 2002 corresponding to SDXC and an SS controller 2004 corresponding to USB 3.0. When the SDHC card is used, the speed of the card interface 2002 is generally less than 480 Mbps, which is the maximum speed of the USB 2.0 mode. Hence, the benefits brought about by the use of the SS mode for connection to the USB host device are small. From the viewpoint of system operation, it would be preferable to connect the device using the USB 2.0 mode so as to save the SS mode bandwidth for other devices requiring high-speed transfer. For example, Japanese Patent Laid-Open No. 2005-327247 has proposed a technique of providing a mechanical switch for switching the transfer unit on the peripheral device (device) side and allowing the user to operate the switch in order to select the data transfer unit to be used in accordance with the operation method.
However, according to the above-described conventional technique, the user must determine whether high-speed transfer is necessary and then manually switch the data transfer unit accordingly. This makes user operation cumbersome.
Embodiments of the present invention provide a communication control technique that more suitably allows for the execution of data transfer when connecting a host device and a device via a connector having a plurality of independent data buses.